Your plant/tree must stay moist for the first two to three weeks and will need to be checked every day during this period. An easy way to do this is to place your finger into the soil about 3 to 4 inches deep to feel for moisture. If the soil feels dry your tree needs watered. Make sure to water long enough to moisten the soil through to the bottom of the roots. It is very important not to let your tree dry out during this time.

Note: Check your tree even during periods of rain, as it may not have received enough moisture to penetrate the bottom of the roots. During heavy rains, water tends to pool and run off, while a light rain will not penetrate deep enough.

During the third water week you may begin to decrease watering to two or three times a week. A clay-based soil may retain more water allowing you to begin watering less, whereas sand based soils may continue to dry out more frequently.
Its imparitive to understand your soil conditions and your plants watering needs. For example:

Bristlecone Pines and Russian Sage are highly resilient to harsh weather and bad soils, therefore are drought tolerant.

Aspens however, like to stay moist and may need watered more frequent.

In addition to the standard watering care as stated above, during the heat of the summer it may be necessary to water your plants one to two times per day for the first two weeks. Especially take notice of hot-dry windy weather conditions, as your plant will become dry far more quickly.

It is recommended during these warmer months to utilize the cooler evening and morning temperatures to plant.

You will need to water your tree or shrub throughout this season when temperatures reach above 50 degrees consistently for a week. This is essential especially when dealing with evergreens.